Metabolic rewiring is an established hallmark of cancer, but the details of this rewiring at a systems level are not well characterized. Here we acquire this insight in a melanoma cell line panel by tracking metabolic flux using isotopically labeled nutrients. Metabolic profiling and flux balance analysis were used to compare normal melanocytes to melanoma cell lines in both normoxic and hypoxic conditions. All melanoma cells exhibited the Warburg phenomenon; they used more glucose and produced more lactate than melanocytes. Other changes were observed in melanoma cells that are not described by the Warburg phenomenon. Hypoxic conditions increased fermentation of glucose to lactate in both melanocytes and melanoma cells (the Pasteur effect). However, metabolism was not strictly glycolytic, as the tricarboxylic acid (TCA) cycle was functional in all melanoma lines, even under hypoxia. Furthermore, glutamine was also a key nutrient providing a substantial anaplerotic contribution to the TCA cycle. In the WM35 melanoma line glutamine was metabolized in the "reverse" (reductive) direction in the TCA cycle, particularly under hypoxia. This reverse flux allowed the melanoma cells to synthesize fatty acids from glutamine while glucose was primarily converted to lactate. Altogether, this study, which is the first comprehensive comparative analysis of metabolism in melanoma cells, provides a foundation for targeting metabolism for therapeutic benefit in melanoma.Metabolism in cancer cells differs from that of normal nonproliferative cells. Perhaps the most common variation from the norm in cancer metabolism is "aerobic glycolysis" or the Warburg effect. Under the Warburg effect, metabolism of glucose is largely fermentative rather than respiratory, with increased production of lactate, in normal atmospheric oxygen conditions (1). This is also associated with increased uptake of glucose, a common characteristic of cancers detectable in tumors in patients via 18 F-deoxyglucose-PET (2). However, the extent to which the Warburg effect represents a rebalancing of metabolism (increasing fermentation while decreasing respiration) versus an amplification of metabolism (increasing fermentation while maintaining, or even increasing, respiration) is the subject of debate (3, 4). The Warburg effect contrasts with the Pasteur effect, in that the latter describes the switch from fermentation to respiration when oxygen is plentiful, and its reversal when oxygen is limiting (5), while the Warburg effect describes fermentative activity of cancer cells irrespective of oxygen. In the progression of tumors, cancer cells are subject to a range of oxygen concentrations, and low oxygen induces hypoxia-inducible factor (HIF), 2 which leads to a metabolic rewiring of cancer cells, resulting in a more glycolytic metabolism (6). Therefore, cancer cells may potentially demonstrate both Warburg and Pasteur effects. Furthermore, beyond glycolysis, altered oncogene expression has strong effects on other branches of central carbon metabolism. For insta...

B cells predominate in a quiescent state until antigen is encountered, which results in rapid growth, proliferation and differentiation. These distinct cell states are likely accompanied by differing metabolic needs, yet little is known about the metabolic control of B cell fate. Here we show that glycogen synthase kinase 3 (GSK3) is a metabolic sensor that promotes the survival of naïve recirculating B cells by restricting cell mass accumulation. In antigen-driven responses, GSK3 was selectively required for CD40-mediated regulation of B cell size, mitochondria biogenesis, glycolysis and reactive oxygen species (ROS) production. GSK3 was required to prevent metabolic collapse and ROS-induced apoptosis when glucose became limiting, functioning in part by repressing c-Myc-dependent growth. Importantly, we found that GSK3 was required for the generation and maintenance of germinal center B cells, which require high glycolytic activity to support growth and proliferation in a hypoxic microenvironment.

p32/gC1qR/C1QBP/HABP1 is a mitochondrial/cell surface protein overexpressed in certain cancer cells. Here we show that knocking down p32 expression in human cancer cells strongly shifts their metabolism from oxidative phosphorylation (OXPHOS) to glycolysis. The p32 knockdown cells exhibited reduced synthesis of the mitochondrial-DNA-encoded OXPHOS polypeptides and were less tumorigenic in vivo. Expression of exogenous p32 in the knockdown cells restored the wild-type cellular phenotype and tumorigenicity. Increased glucose consumption and lactate production, known as the Warburg effect, are almost universal hallmarks of solid tumors and are thought to favor tumor growth. However, here we show that a protein regularly overexpressed in some cancers is capable of promoting OXPHOS. Our results indicate that high levels of glycolysis, in the absence of adequate OXPHOS, may not be as beneficial for tumor growth as generally thought and suggest that tumor cells use p32 to regulate the balance between OXPHOS and glycolysis.Tumors can be distinguished from their nonmalignant counterparts by specific molecular signatures expressed in malignant cells and tumor vasculature. We explore such differences by identifying tumor-homing peptides from phage libraries that we screen in vivo (60). We recently showed (19) that the cellular receptor for one of our tumor-homing peptides is a protein variously known as p32, p33, gC1q receptor (gC1qR), or hyaluronic acid binding protein 1 (HABP1). This protein was originally isolated based on its copurification with the nuclear splicing factor SF-2 (37). However, it was subsequently shown to bind also the globular heads of complement component C1q (23), hyaluronic acid (10), and numerous other extracellular and intracellular proteins (24,28,33,42). Most recently it has been shown that p32 interacts with the long and short forms of the tumor suppressor ARF (30,56,57). Despite the numerous reports on p32 interaction partners, the role of these binding activities in the physiological function of the protein is unknown, and some investigators have proposed that p32 may be a chaperone protein (58,65).The p32 protein is primarily localized in the mitochondrial matrix (12, 46, 48) but has also been reported to be present in other subcellular locations (53). Some of the p32 protein can be at the cell surface, a location that appears to be specific for tumors (19). In this regard, p32 is similar to some other intracellular proteins that are also partially localized at the cell surface in tumor cells (8,49). In addition to the partial cell surface localization of p32, many human tumors exhibit higher p32 expression levels than their nonmalignant counterpart tissues (7, 19, 52, 59). Moreover, p32 is differentially expressed during the progression of epidermal carcinoma, accumulating in metastatic islands (25).We set out to modulate p32 expression in tumor cells to gain information on the role of this protein in cancer. We show here that p32 knockdown cells shift their metabolism from oxidative phosph...